1. Field of the Invention
The present invention relates to a zoom lens which is used for an image pickup apparatus such as a digital camera, a video camera, a TV camera, or a film camera.
2. Description of the Related Art
As an image pickup optical system which is used for an image pickup apparatus such as a video camera or a digital still camera using a solid-state image pickup element, a zoom lens having a wide field angle and a high zoom ratio and also a high optical performance in a whole zoom range and in an overall object distance is required. Further, the zoom lens is required to have an anti-shake function which corrects an image shake generated by a camera shake or a hand jiggling.
A zoom lens which is constituted by four lens units having positive, negative, positive, and positive refractive powers in order from an object side to an image side is known (Japanese Patent Laid-open No. 2003-322795, and U.S. Pat. No. 6,975,461).
A zoom lens which is constituted by four lens units having positive, negative, positive, and positive refractive powers in order from the object side to the image side and is configured to move each lens unit to perform a zoom operation and also to have a part of the lens units functioned as an anti-shake lens unit is known (U.S. Pat. No. 7,268,954).
Further, a zoom lens which is constituted by five lens units of positive, negative, positive, negative, and positive powers in order from the object side to the image side, and is configured to move each lens unit to perform a zoom operation and also to have a part of the lens units functioned as an anti-shake lens unit is known (Japanese Patent Laid-open No. 2006-227526).
Commonly, in a zoom lens, a high zoom ratio can be obtained by a predetermined movement amount if a refractive power of a magnification varying lens unit is strengthened. Although the high zoom ratio is easily obtained by strengthening the refractive power of the magnification varying lens unit, an aberration variation caused by the zoom operation (magnification varying operation) becomes large and it is difficult to obtain a good optical performance in a whole zoom range. In order to widen the field angle, a zoom type may be configured so that a refractive power arrangement of a whole system becomes a retro-focus type in a zoom range at the wide-angle side. Although the field angle of the retro-focus type is easily widened, a large amount of an off-axis aberration is easily generated and it is difficult to obtain a high optical performance in a whole field angle because a whole lens system is asymmetric with respect to an aperture stop. On the other hand, as an anti-shake method of correcting an image shake caused by a hand jiggling, a method of moving a part of lens units of the zoom lens in a direction perpendicular to the optical axis does not have to add an optical system for the anti-shake operation and therefore it has an advantage that can easily perform the anti-shake operation. However, a space for arranging the anti-shake lens units is necessary and an decentration aberration is generated in performing the anti-shake operation, and therefore an image quality is deteriorated.